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Study of High-gradient Structures for the Linear Collider

Research Project

Project/Area Number 03044141
Research Category

Grant-in-Aid for international Scientific Research

Allocation TypeSingle-year Grants
SectionJoint Research
Research InstitutionNational Laboratory for High Energy Physics (KEK)

Principal Investigator

TAKATA Koji  National Laboratory for High Energy Physics (KEK), 加速器研究部, 教授 (10044760)

Co-Investigator(Kenkyū-buntansha) J.MADSEN  CERN, PS, 主研
I. WILSON  CERN, SL, 主研
W. SCHNELL  CERN, CLIC, 主幹
K. HUBNER  CERN, PS, 主幹
SHINTAKE Tsumoru  National Laboratory for High Energy Physics (KEK), 加速器研究部, 助手 (90162792)
HIGO Toshiyasu  National Laboratory for High Energy Physics (KEK), 加速器研究部, 助手 (10156581)
MIZUNO Hajime  National Laboratory for High Energy Physics (KEK), 加速器研究部, 助教授 (80044775)
TAKEDA Seishi  National Laboratory for High Energy Physics (KEK), 加速器研究部, 助教授 (40029898)
KIMURA Yoshitaka  National Laboratory for High Energy Physics (KEK), 加速器研究部, 教授 (00010794)
MADSEN J.  CERN
WILSON I.  CERN
SCHNELL W.  CERN
HUEBNER K.  CERN
MADSEN J.  CERN, PS, 主研
WILSON I.  CERN, SL, 主研
SCHNELL W.  CERN, CLIC, 主幹
HUBNER K.  CERN, PS, 主幹
Project Period (FY) 1991 – 1992
Project Status Completed (Fiscal Year 1992)
Budget Amount *help
¥9,000,000 (Direct Cost: ¥9,000,000)
Fiscal Year 1992: ¥5,000,000 (Direct Cost: ¥5,000,000)
Fiscal Year 1991: ¥4,000,000 (Direct Cost: ¥4,000,000)
Keywordslinear collider / linac / klystron / high gradient acceleration / high electric field / dark current / oxygen free copper / precision machining / リニアコライダ- / 加速管 / 高電界加速 / 無酸素銅ろう付 / 電界放出電子
Research Abstract

Experimental and theoretical studies have been carried out for accelerating structures of the main linac of linear colliders. The structure is of a traveling wave type driven with 11.4GHz X-band RF power. The accelerating gradient is desired to be as high as 100MV/m. In this fiscal year, we fabricated a proto-type structure of oxygen free copper with a very accurate and fine surface finish. It was then high power tested at KEK by using a 30MW klystron which had been developed at KEK. We were able to reach the high gradient after a 500 hour conditioning. We also made detailed measurements of dark currents due to surface emission under the very high RF electric field.
In order to achieve a high gradient, a high power klystron is absolutely necessary. However, the fabrication technology of klystrons becomes extremely difficult as the operation frequency raises. Therefore high gradient experiments were carried out at the S-band(2.86GHz), at which frequency the high power klystrons are easil … More y available. In fact at this frequency we achieved over 80MV/m average gradients successfully and also tested beam acceleration too. For the TeV energy linear collider, however, the RF frequency should be an X-band(11.4GHz) one at the lowest, since otherwise the total ac power becomes impractically high. KEK has been developing X-band high power klystron for a long time, and recently we succeeded to get a first tube which can deliver 30MW RF power. This experiment is carried out by using this tube.
CERN has a different idea for the TeV linear collider. Particularly they are considering a K-band(30GHz) frequency generated by a FEL. Its realization is still far in the future. They are, on the other hand, developing technologies to fabricate accelerating structure which is capable of such high gradients. They are therefore wanting to test the structure as soon as possible even at lower frequencies. Hence a joint experiment started at KEK.
In this experiment CERN and KEK made structures of the same dimensions. The main specification is : number of cell 20, coupler cell 2, cell length 2.9mm, phase shift per cell 2pi/3, constant impedance structure, beam aperture 6mm, cell diameter 10.4mm, disk thickness 1mm. The Q value is 6500, attenuation is 1.54/m, impedance is 104MOMEGA/m. The maximum surface field over the beam aperture is 3.9 times the average gradient. The most critical point in the fabrication was to achieve a sufficient smoothness on the beam aperture. It is accomplished by carefully choosing diamond bits. We also paid attention to avoid metallic and organic dusts falling inside the structure. They are usually a serious cause to limit the maximum attainable gradient by inducing heavy discharges.
The test was carried out at the klystron repetition rate 50Hz. The RF pulse length was typically 100ns. The KEK structure reached 70MV/m after 60million pulses, While the CERN one did 100MV/m after 9 million pulses. In the CERN case, we also used a SLED system to boost the RF power.
Observed dark currents were analized by use of a modified Fowler-Nordheim formula. The important measure therein is the field enhancement factor beta. For ther both structures, we obtained similar values around 50 for beta.The absolute value of the dark current was found to be rather high for the KEK structure and further studies are necessitated to resolve this. Less

Report

(2 results)
  • 1992 Final Research Report Summary
  • 1991 Annual Research Report
  • Research Products

    (16 results)

All Other

All Publications (16 results)

  • [Publications] 山本 昇 外: "″Beam Size Stabilization in the JLC Final Focus System with Dispersion Free Orbit Correction″" KEK Preprint. 92-60. 1-3 (1992)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] 生出 勝宜: "″Final Focus System with Odd-Dispersion Scheme″" KEK Preprint. 92-58. 1-3 (1992)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] 浦川 順治 外: "″The Development of RF Reference Lines and a Timing System for Japan Linear Collider″" KEK Preprint. 92-8. 1-4 (1992)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] 新竹 積: "″The Choke Mode Cavity″" KEK Preprint. 92-51. 1-11 (1992)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] 肥後 寿泰 外: "″High Gradient Experiment for X-band Travelling Wave Structure″" KEK Preprint. 92-99. 1-3 (1992)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] 肥後 寿泰 外: "″Damped Structure for JLC X-band Linac″" KEK Preprint. 92-122. 1-3 (1992)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] N.Yamamoto et al: "Beam Size Stabilization in the JLC Final Focus System with Dispersion Free Orbit Correction" KEK Preprint. 92-60. 1-3 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] K.Oide: "Final Focus System with Odd-dispersion Scheme" KEK Preprint. 92-58. 1-3 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] J.Urakawa et al: "The development of RF Reference Lines and a Timing System for Japan Linear Collider" KEK Preprint. 92-8. 1-4 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] T.Shintake: "The Choke Mode Cavity" KEK Preprint. 92-51. 1-11 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] T.Higo et al: "High Gradient Experiment for X-band Traveling Wave Structure" KEK preprint. 92-99. 1-3 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] T.Higo et al: "Damped Structure for JLC X-band Linac" KEK Preprint. 92-122. 1-3 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] 新竹 積: "Proposal of a nanometer beam size monitor for e^+e^ー linear colliders" Nuclear Instruments and Methods in Physics Research. A311. 453-464 (1992)

    • Related Report
      1991 Annual Research Report
  • [Publications] 竹田 誠之: "Xーband klystron modulator for the Accelerator Test Facility" Proceedings of the 1991 Particle Accelerator Conference (San Francisco). (1992)

    • Related Report
      1991 Annual Research Report
  • [Publications] 肥後 寿泰,高田 耕治: "Xーband accelerating structure for Japan Linear Collider" Proceedings of the 1991 Particle Accelerator Conference (San Francisco). (1992)

    • Related Report
      1991 Annual Research Report
  • [Publications] 水野 元,肥後 寿泰: "Development of Xーband high power pulsed klystron" Proceedings of the 16th Linear Accelerator Meeting in Japan. (1991)

    • Related Report
      1991 Annual Research Report

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Published: 1991-04-01   Modified: 2016-04-21  

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